The present invention relates to a temperature sensor mounting structure, and more particularly, to a structure for mounting a temperature sensor, which detects the temperature of a wall surface, and a video projector to which the structure is applied.
In a video projector using a liquid crystal light bulb, such as a three-panel type liquid crystal projector, a control circuit receives an image signal from a personal computer (PC), video equipment, and the like. The control circuit converts the received image signal to a predetermined voltage and supplies the voltage via signal lines to liquid crystal light bulbs for red light, green light, and blue light. A drive voltage corresponding to the image signal is applied to each pixel for each liquid crystal light bulb to vary the transmissivity of each pixel in accordance with the image signal and modulate the light from a lamp. This generates an image on a screen. A light source that generates a large amount of light, such as metal halide lamp, is normally used as such lamp. Thus, a large amount of power is supplied from a power supply through a power supply line. This heats the lamp to a high temperature.
The radiation or transfer of the heat generated by the lamp raises the temperature of a resin housing, such as a lamp housing that forms an optical path. Further, the liquid crystal in a liquid crystal panel forming the light crystal light bulb and polarization plates arranged at an entrance side and exit side of the liquid crystal panel absorbs light. This raises the temperature of the liquid crystal and polarization plates. Thus, cooling air is supplied to these parts to prevent the temperature from rising. However, if a cooling fan stops operating or an intake port for the cooling air is clogged, the temperature of the resin wall surface of the lamp housing or the polarization plate may exceed a predetermined temperature. To prevent such rise in temperature, a temperature sensor is used to detect the temperature of a wall surface of the lamp housing or a wall surface of a resin polarization plate holder, which holds the polarization plate. Further, when the temperature of these wall surfaces become higher than or equal to a predetermined temperature, a temperature protector stops the supply of power to the lamp and prevents the temperature from rising.
In this manner, temperature sensors, which detect the temperature of a wall surface, are normally arranged at several locations in a video projector that uses liquid crystal light bulbs. Japanese Laid-Open Patent Publication No. 2003-43440 describes a prior art example of a structure for mounting a temperature sensor that detects the wall surface temperature. The structure will now be described with reference to FIG. 1.
FIG. 1 is an exploded perspective view showing a structure in the prior art for mounting a temperature sensor on an entrance side polarization plate holder in a video projector using liquid crystal light bulbs. Referring to FIG. 1, a polarization film 112 is adhered to a transparent base material 111, such as glass, to form a polarization plate 110. The polarization plate 110 is held on a polarization plate holder 120 by a plurality of guide portions 121. A generally U-shaped pressing plate 122 is fitted onto a cutout portion 123 formed in the polarization plate holder 120. The pressing plate 122 restricts the upward movement of the polarization plate holder 120 and has an open lower end that is spread open. In this manner, the polarization plate 110 is mounted on the polarization plate holder 120.
The upper left part of the wall surface on the polarization plate holder 120, as viewed in the drawing, serves as a temperature-detected wall surface, the temperature of which is detected by the main body of a temperature sensor 100. The main body of the temperature sensor 100, which is thin and has the shape of a rectangular plate, includes a temperature detection surface. The main body of the temperature sensor 100 is attached to a sensor fastening plate 130 so that the temperature detection surface of the main body of the temperature sensor 100 is pressed against the surface of the polarization plate holder 120. The sensor fastening plate 130 includes a fastening portion 131 and a mounting portion 132. The fastening portion 131 is fitted onto the main body of the temperature sensor 100 and presses the temperature detection surface on the main body of the temperature sensor 100 against the wall surface of the polarization plate holder 120. The mounting portion 132 is coupled to a tab 124 extending from the polarization plate holder 120. The tab 124 of the polarization plate holder 120 includes a threaded hole 125, and the mounting portion 132 includes a hole 133 aligned with the threaded hole 125. A screw 134 is inserted through the hole 133 and mated with the threaded hole 125 through the hole 133 to mount the temperature sensor 100.
The polarization plate holder 120, to which the polarization plate 110 and the temperature sensor 100 are mounted as described above, is held on an optical box 140 by guides 141. A bent piece 127 including holes 128 extends from the upper end of the polarization plate holder 120. Screws 129 are inserted through the holes 128 of the bent piece 127 and mated with threaded holes 142 formed in the optical box 140 to fasten the polarization plate holder 120 to the optical box 140.
However, in the conventional structure for mounting the temperature sensor, which detects the wall surface temperature, the sensor fastening plate 130, which is a discrete component, is used to press the main body of the small, rectangular plate-shaped temperature sensor 100 against the wall surface of the polarization plate holder 120 that serves as the temperature-detected wall surface. Thus, the mounting of the temperature sensor 100 is difficult. Furthermore, the sensor fastening plate 130, one end of which is fastened to the tab 124, must be elastic to press the small, plate-shaped temperature sensor 100 against the wall surface of the polarization plate holder 120. This makes it difficult to select the appropriate material for the sensor fastening plate 130. More specifically, if the sensor fastening plate 130 was to be formed from an elastic metal plate, heat would be conducted through the sensor fastening plate 130 and thereby lower the accuracy of the temperature detected on the wall surface of the polarization plate holder 120. To avoid such heat conductance, the sensor fastening plate 130 may be formed by a resin molded product. However, the elasticity of the sensor fastening plate 130 would be insufficient and it may be difficult to constantly press the surface of the temperature sensor 100 against the wall surface of the polarization plate holder 120. This would also lower the temperature detection accuracy.
Therefore, it would be desirable to provide a structure for mounting a temperature sensor that facilitates the mounting of the temperature sensor while enabling accurate temperature detection of a temperature-detected wall surface. Further, it would be desirable to provide a video projector using such structure for mounting the temperature sensor.